The word "battery", as used in this context, pertains to one or a connected set of similar units or cells acting as an electrical energy source. A nuclear battery, also known as an atomic battery, refers to a battery in which the source of energy is the energy stored in the nucleus of the atoms of the fuel. The nuclear energy stored in the nucleus is typically released in one of three ways: fission of the nucleus, fusion of the nucleus, or radioactive decay of the nucleus. Nuclear batteries according to the present invention rely on radioactive decay of nuclei and convert to electrical energy the liberated nuclear radiation (beta particles) energy. Over the last several decades a number of nuclear batteries of the kind relying on nuclear radioactive decay have been developed on the basis of a single conversion process or a double conversion process. Single conversion nuclear batteries directly convert nuclear radiation into electrical energy. Double conversion nuclear batteries convert nuclear radiation energy into an intermediate form of energy which in turn is converted into electrical energy.
Nuclear batteries of the single conversion type include betavoltaic batteries, wherein a semiconductor p-n junction is exposed to nuclear radiation which results in the production of electron-hole pairs and thus an induced current at low voltage. An example is afforded in U.S. Pat. Nos. 2,745,973 and 4,024,420. Another example of single conversion process nuclear batteries is a low voltage battery that uses the principle of gas ionization, wherein the battery consists of an ionization gas, two different electrodes which establish an electric field in the gas space, and a nuclear radiation source which is either gaseous or solid in form. Still another example is afforded by a high voltage, vacuum battery in which one electrode forms the source of charged particle nuclear radiation while the other electrode is chosen to have low secondary emission and high collection efficiency, thus resulting in a high voltage, low current device.
Nuclear batteries of the double conversion process type include photovoltaic batteries (in which the nuclear radiation energy is first converted into electromagnetic radiation, typically by irradiating a phosphorescent material and then exposing a semiconductor p-n junction to electromagnetic radiation to produce low voltage electrical current) and thermoelectric batteries (wherein the nuclear radiation is converted into thermal energy which in turn is converted to electrical energy by means of the Seebeck effect or thermoelectric conversion). Examples of nuclear/photovoltaic batteries are disclosed in U.S. Pat. Nos. 4,628,143; 4,900,368; and 5,008,579.
Energy conversion processes are generally quite inefficient. The single conversion process nuclear batteries have conversion efficiencies typically of the order of 5% or lower. Nuclear batteries using the double conversion process are even more inefficient. The practical limitations on the single conversion betavoltaic, semiconductor battery include significant attenuation in the nuclear radiation energy prior to reaching the semiconductor and further attenuation in energy as the nuclear radiation propagates through the semiconductor, en route to the depletion region.
It is accordingly an object of the present invention to provide a nuclear powered battery having a conversion efficiency superior to presently available single and double conversion nuclear batteries.
It is a further object of the present invention to provide a nuclear powered battery which may be fabricated as an integral part of and provide electrical energy for an integrated circuit.
It is a further object of the present invention to provide a useful article, a nuclear powered battery, in which radioactive tritium, a by-product from nuclear reactors, is chemically bound and thus immobilized in a body of amorphous silicon, thereby making advantageous use of tritium stored in safety facilities.